Add ip6 dummy address to keep data usage stats consistent.

Because of the way the tunnel pumps packets into the networking
stack, the netfilter xt_qtaguid module can't track stats
accurately: the totals don't add up.
With "clat" having an ip address, qtaguid will track stats
against it, which then can be deducted from the external iface.

Bug: 11687690
Change-Id: I22ebf26dd9249e821da87665d2bfb0e54d3cdf64
4 files changed